This invention relates in general to the field of display instruments, and in this case the specific field of displays which present images or information which in the normal cases is composed of a plurality of individual pixels, and in which, at a sufficient distance from the display, the individual pixels optically merge into a single overall image. In particular the invention relates to such displays in which the representation is based on the use of fluids, which are also called fluidic displays.
In concrete terms the invention relates to a device for the pixel-integrated return of fluid in the pixel of a fluidic display, and is characterized in that the fluid with which the desired information is to be displayed and/or the carrier fluid in which the first fluid is optionally embedded can be returned in a particularly compact manner and invisibly for an observer past the visible portion of a pixel (image compartment) into a reservoir (reservoir compartment) through or out of said reservoir.
The prior art describes display instruments which, for the presentation of images or information, use colored, e.g. black fluids which, depending on the state of the individual pixel, are visible, i.e. “turned on”, or invisible, i.e. “turned off”. Different technologies can be used for the switching of the image. One requirement that all the technologies have in common is that the colored fluid must be able to assume the states “visible” and “invisible”. For the switch from “on” to “off”, the fluid can change either its color or its contrast or disappear from the field of vision of an observer. This process must also be reversible, so that the fluid can change back into the “on” state.
For the case of the disappearance of the fluid from the observer's field of view, the fluid must be moved. The prior art also describes various technologies for this purpose. Special preference is given to pumps or the electrowetting effect. In general, the colored liquid is embedded in an additional fluid with which it is immiscible, so that a two-phase mixture is formed. Devices are also known in which the carrier fluid is a fluid such as oil, for example, as well as devices in which the colored fluid is in a gaseous carrier fluid, such as in air or a cover gas, for example.
The colored fluid is first located in a space provided for the purpose, the contents of which are visible to an observer. This space is referred to below as the image compartment. For the displacement of the colored fluid from the observer's field of view, sufficient space must be provided to hold the fluid temporarily, namely until the next change of the switching state of the pixel to “on”. In the normal case, this space is provided in the form of an appropriately sized reservoir which is located outside the observer's field of view. To allow the fluid to get into this reservoir, which is also called the reservoir compartment below, a corresponding connecting duct must also be provided which connects the pixel or the image compartment with the reservoir or the reservoir compartment. The connecting duct can thereby be realized both without and with a taper.
If the fluid is transported by a means that works unidirectionally such as, for example, a one-way pump, it must be possible to transport the colored fluid and optionally the carrier fluid in a circuit, unless the fluid is to be transported into and out of the observer's field of view only once. As a result of the rotating change of colored fluid and (colorless) carrier fluid, the pixel is turned on and off. In this context, we can speak of the connecting duct as well as of a return duct, because the liquids or fluids are returned through this duct in the circuit to the pixel, i.e. into the image compartment.
The problem thereby encountered is that sufficient space must be provided for the above mentioned return duct. At least the return duct plus the reservoir must be sized so that both together can hold all of the colored fluid, so that the fluid can disappear completely from the observer's field of view or from the image compartment.
In the case of a flat construction, in which it is impossible to work in any depth and to thereby take advantage of the third dimension, the inescapable result is that the reservoir compartment and return duct together take up at least as much surface area as the actual (visible) pixel or the image compartment. Consequently there is an unsatisfactory ratio between active (i.e. optically switchable) and inactive (i.e. optically invariable) surface area. The result is poor contrast and a resolution that is in need of improvement (number of pixels per unit of area).
To resolve the problem of the high consumption of surface area, it is desirable to transport the colored fluid and optionally the carrier fluid in one and the same duct, whereby in this regard care must be taken to ensure that the two fluids are not mixed with one another. An approach of this type is described, for example, in L. Riegger et al.: “MICROFLUDICS ON A CONVENTIONAL, 10-$ CD-ROM DRIVE: ALL-IN-ONE DETERMINATION OF THE HEMATOCRIT”; The 10th International Conference on Miniaturized systems for Chemistry and Life Sciences (μTAS2006), Nov. 5-9, 2006, Tokyo, Japan. The authors use a blind duct with a rounded end, which on account of a specified shaping pulls fluid which is input on one edge in the opening area of the duct by means of the capillary effect first on one wall of the duct toward the closed end, whereby the fluid then flows back to the opposite wall, and only after the wall has been almost completely wetted is the remaining gas inside the duct displaced toward the output. The background of the invention is the desire to be able to fill a blind duct of this type without bubbles. As a result of this skillful utilization of the capillary effect, it is therefore temporarily possible to contain two fluid paths flowing past each other in parallel in a single duct volume, without the requirement for partitions or other separating walls. However, the shape of the duct is selected so that the duct is ultimately completely filled by the fluid, whereby the fluid fronts come into contact and finally merge with each other. However, this mixing is not desirable with regard to the problem addressed by the current invention, because the colored fluid and the carrier fluid must remain separated from each other at all times.